Atrial fibrillation
How disorganised electrical activity replaces the sinus rhythm, why the ventricles beat irregularly, what losing the atrial kick costs, and why stasis in the left atrial appendage can lead to a stroke.
By the end, you can
- Describe normal conduction from the sinu-atrial node through the atrioventricular node.
- Explain how triggers and an altered atrium start and sustain atrial fibrillation.
- Explain why the ventricular response is irregularly irregular and often fast.
- Relate loss of the atrial kick to reduced filling and symptoms.
- Explain how a thrombus forms in the left atrial appendage and can cause a stroke.
- Recognise the classic appearances, scores and tests of atrial fibrillation, and explain how anticoagulation, rate control and rhythm control act on its mechanism.
What it is
Atrial fibrillation (AF) is an arrhythmia in which disorganised electrical activity replaces the regular impulses from the sinu-atrial node, so the atria quiver instead of contracting and the ventricles respond irregularly. It is the most common sustained arrhythmia, and it is classified by how long episodes last.
3 types to tell apart
- Paroxysmal AF
- Episodes that stop on their own or with treatment, usually within seven days.
- Persistent AF
- AF lasting longer than seven days; called long-standing persistent after a year.
- Permanent AF
- Sinus rhythm is not restored, or no further attempt is made to restore it.
US spelling: fibres → fibers.
Normal function
Sinus rhythm
In sinus rhythm each beat starts in the , which fires about 60–100 times a minute at rest. The impulse spreads across both atria, along the and the to the left atrium, and the atria contract together: the P wave on the ECG.
A fibrous skeleton insulates the atria from the ventricles, so the only route onwards is the . It conducts slowly, delaying the impulse by about a tenth of a second so the atria finish emptying before the ventricles contract. Its refractory period also limits how many impulses it can pass each minute.
The impulse then runs rapidly down the , the bundle branches and the Purkinje fibres, so the ventricles contract together and the QRS complex is narrow. Atrial contraction at the end of diastole (the atrial kick) adds the last part of ventricular filling.
Underlying change · Step 1 of 4
Triggers and a vulnerable atrium
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Disrupted function · Step 2 of 4
Chaos in the atria, irregular ventricles
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Disrupted function · Step 3 of 4
Loss of the atrial kick
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Consequences · Step 4 of 4
Stasis in the appendage and stroke
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Symptoms and signs
Symptoms, signs and findings
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Exam detail
Exam detail
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Treatment
How treatment works
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Recap
Recap
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Self-check
Check your understanding
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .